Charging of users for data transmission in a wireless communication system provides a means for operators to exploit business models that are intended to bring profit to the operators.
Within Third Generation Partnership Project (3GPP), attempts are made on realizing a tighter integration/aggregation between different accesses, e.g. between 3GPP access and Wireless Local Area Networks (WLANs) access, between legacy LTE access and Fifth Generation (5G) access, between access via licensed spectrum and unlicensed spectrum.
Before briefly outlining scenarios for abovementioned accesses, an overview of charging according to 3GPP is provided.
FIG. 1 is an overview of a so called Evolved Packet Core (EPC) architecture. This architecture is defined in 3GPP Technical Specification (TS) 23.401, in which e.g. PGW (Packet data network GateWay), SGW (Serving Gateway), PCRF (Policy and Charging Rules Function), MME (Mobility Management Entity) and mobile device (UE) are defined and described. An LTE radio access, e.g. Evolved Universal Terrestrial Radio Access Network (E-UTRAN), includes one more so called eNBs, common referred to as base stations.
The SGW acts as an anchor point for wireless device mobility. Moreover, the SGW also includes functionalities, such as temporary downlink data buffering while the UE is being paged, packet routing and forwarding to the right eNB.
The PDN-GW is responsible for tasks such as IP (Internet Protocol) address allocation for the UE, and Quality of Service (QoS) enforcement in the downlink.
The MME handles the access network, while being responsible for tasks such as idle mode tracking of the UEs, paging, retransmission, bearer activation/deactivation, etc.
The PCRF determines policy rules in real-time with respect to the UEs of the system. This may e.g. include aggregating information in real-time to and from the core network and operational support systems, etc. of the system so as to support the creation of rules and/or automatically making policy decisions for user radio terminals currently active in the system based on such rules or similar.
The HSS manages and holds subscription related information in order to support handling of calls and/or data sessions.
The eNBs provides both user plane and control plane protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME interface and to the Serving Gateway (S-GW) by means of the S1-U interface. The eNB contains for example functions for Radio Resource Management including Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in uplink, downlink and sidelink (scheduling). In addition, the eNB selects an MME for the UE at attach and routes user plane traffic towards the SGW.
Aforementioned FIG. 1 shows the architecture for 3GPP accesses. In those accesses the radio interface is specified by 3GPP, e.g. LTE.
With reference to FIG. 2, there is shown an extension to the EPC architecture in order to allow also non-3GPP accesses. For non-3GPP accesses, air interfaces are not specified by 3GPP, e.g. WLAN. Reference is made to 3GPP TS 23.402 in this respect.
As shown in FIG. 2, usage of a non-3GPP access is visible in the CN, e.g. in the PGW via the S2a and S2b interfaces.
The EPC in 3GPP defines what is called a Policy and Charging Control (PCC) architecture with advanced tools for service-aware Quality of Service (QoS) and charging control on a per-service basis. The main entities of this architecture are shown in FIG. 3. For more details refer to the 3GPP TS 23.203 Policy and Charging Control Architecture.
In the PCC architecture, the PCRF is making decisions about charging depending on the flow being established, e.g. if it is offline or online charging. Therefore, the PCRF needs to be able to keep itself up-to-date about events taking place in the access network. To achieve this, procedures have been defined that allow the PCRF to notify a Policy and Charging Enforcement Function (PCEF) and/or a Bearer Binding and Event Reporting Function (BBERF) about which events the PCRF is interested in. In PCC terminology, the PCRF is said to subscribe to certain events, and that the PCEF/BBERF sets the corresponding event triggers. When an event occurs, and the corresponding event trigger is set, the PCEF/BBERF will report the event to the PCRF and allow the PCRF to revisit its previous policy decisions.
The PCRF is the central entity making PCC decisions based on different inputs:                Operator configuration in the PCRF that define the policies applied to given services        Subscription information/policies for a given user, received from the SPR        Information about the service from the AF        Information from the access network about what technology is used for a particular user equipment (can change only during handover today), etc.        
Moreover, a charging functionality for keeping track of traffic usage by subscribers is located at the PCEF.
As mentioned, with the PCC architecture, charging can be performed as offline charging or as online charging, which will be described in the following.
For offline charging, the PCEF is placed at the PDN Gateway to perform measurements of user plane traffic, e.g. user plane traffic volume and/or time duration of a session. These measurements are configured via policies sent by the PCRF over the Gx reference point (also referred to as Gx interface) e.g. if a given flow should be charged based on volume, time, etc. The PCRF may also send events so the charging can be adapted. These policies are typically obtained at the User Data Repository (UDR).
Based on these measurements, policies and events the PCEF generates charging events later reported to an OFfline Charging System (OFCS). The charging events are sent to the OFCS, where they are formatted into Charging Data Records (CDRs) and sent further on to the billing system at the Business Support System (BSS) domain.
In addition, the PDN Gateway collects charging information per PDN Connection and per bearer e.g. for inter-operator settlement purposes.
Online charging is handled by an Online Charging System (OCS) that is a credit management system for pre-paid charging. In this case, the PCEF interacts with the OCS to check out credit and report credit status via Gy reference point (also referred to as Gy interface), as shown in FIG. 3.
With online charging, the charging information can affect, in real-time, the services being used and therefore a direct interaction of the charging mechanism with the control of network resource usage is required. The online credit management allows an operator to control access to services based on credit status. For example, there has to be enough credit left with the subscription in order for the service session to start or an ongoing service session to continue. The OCS may authorize access to individual services or to a group of services by granting credits for authorized IP flows. Usage of resources is granted in different forms. The OCS may, for example, grant credit in the form of certain amount of time, traffic volume or chargeable events. If a user is not authorized to access a certain service, for example, in case the pre-paid account is empty, then the OCS may deny credit requests and additionally instruct the PCEF to redirect the service request to a specified destination that allows the user to re-fill the subscription.
Referring once more to FIG. 3, in the case of online charging the PCC rules are sent by the PCRF to the PCEF. The PCEF will enforce the policy decision according to the received PCC rule. All user plane traffic for a given subscriber and IP connection passes through the network entity where the PCEF is located. If the PCC rule specified that online charging shall be used for this PCC rule, the PCEF contacts the OCS via the Gy reference point to request credit according to the measurement method specified in the PCC rule.
As further background information, network connections, bearers and flows will now be described.
3GPP defines a concept of a Packet Data Network (PDN). The PDN is typically an IP network, e.g. Internet or an operator IP Multimedia Subsystem (IMS) service network. A PDN has one more names, where each name is defined in a string called APN (Access Point Name). The PGW is a gateway towards one or more PDNs. A UE may have one or more PDN connections.
A PDN connection is a logical connection between UE and PGW carrying IP traffic, providing the UE access to a PDN. The setup of a PDN connection is initiated from the UE. Each PDN connection has a single IP address or prefix or may have a pair of IPv4 address and IPv6 prefix. The PDN connection can be setup over a 3GPP access (see e.g. TS 23.401 section 5.3.2 and 5.10.2) or over a non-3GPP access (see e.g. TS 23.402 section 7.2 and 16.2). A UE may have one or more PDN connections over a 3GPP accesses, or one or more PDN connections over a non-3GPP access, or both simultaneously.
Every PDN connection consists of one or more bearers. See TS 23.401 section 4.7.2 for a description of the bearer concept. A bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PGW. Each bearer on a particular access has a unique bearer ID. The bearer IDs assigned for a specific UE on S2a/S2b are independent of the bearer IDs assigned for the same UE on S5 and may overlap in value.
On the 3GPP access, the bearer is end-to-end between UE and PGW. The bearer ID is known by PGW, MME, eNB and UE. On the non-3GPP access, there is typically no bearer concept between UE and TWAG/ePDG. The bearer concept is then only defined between PGW and TWAG/ePDG; i.e. it is only defined over S2a/S2b. In this case, the bearer ID is known by PGW and TWAG/ePDG but not by the UE. Regardless of access type, the PCRF is not aware of bearer IDs.
Every PDN connection has at least one bearer and this bearer is called the default bearer. All additional bearers on the PDN connection are called dedicated bearers.
A bearer carries traffic in the form of IP packets. Which traffic is carried on a bearer is defined by filters. A filter is an n-tuple where each element in the tuple contains a value, a range, or a wildcard. An n-tuple is also known as an IP flow.
An example of a 5-tuple is (dst IP=83.50.20.110, src IP=145.45.68.201, dst port=80, src port=*, prot=TCP). This 5-tuple defines a source and destination IP address, a source and destination port, and a protocol. The source port is a wildcard. Traffic matching this 5-tuple filter would be all TCP traffic from IP=145.45.68.201 to IP=83.50.20.110 and port=80.
A traffic flow template, TFT, contains one or more filters. Every bearer has a TFT. One bearer within a PDN connection and access may lack an explicit TFT (this bearer is typically the default bearer). Implicitly such bearer has a TFT with a single filter matching all packets.
Now returning to the aggregation between 3GPP access and WLAN access, this work is called LTE/WLAN Aggregation (LWA) in 3GPP and, since the aggregation is performed at a Radio Access Network (RAN) layer, scheduling and flow control of the data on WLAN or 3GPP links can be controlled by considering dynamic radio network conditions.
Within the scope of 3GPP Release-13, there has been a growing interest in realizing tighter integration/aggregation between 3GPP and WLAN, for example, the same way as carrier aggregation between multiple carriers in 3GPP, where the WLAN is used just as another carrier.
E-UTRAN supports LWA operation whereby a UE in RRC_CONNECTED is configured by the eNB to utilize radio resources of LTE and WLAN. The eNB supporting LWA is connected to WLAN via an ideal/internal backhaul in the collocated deployment scenario or a non-ideal backhaul in the non-collocated deployment scenario. The overall architecture for the LWA is illustrated in FIG. 4. The WLAN Termination (WT) terminates the Xw interface.
In view of charging, a disadvantage is thus that charging cannot be performed while taking the radio resource used, i.e. LTE or WLAN, into account.
In the above scenario, the WLAN is expected to have a Xw interface that is not existing in some known WLANs, referred to as legacy WLANs herein. Therefore, there is also an ongoing work item in 3GPP to support the LWA for legacy WLANs. The related solution is called LTE-WLAN IP Tunneling (LWIP). This work is called as LTE-WLAN RAN Level Integration supporting legacy WLAN. An idea is accordingly that the WLAN network should not be functionally impacted, i.e. no specific support for any Xw-interface or the like shall be needed in the WLAN. Also in this case, the aggregation between LTE and WLAN is not visible in the CN, i.e. neither in MME nor SGW. Consequently, the LWIP has the same disadvantage as LWA.
In the following scenario, the same disadvantage has also been identified. LTE Licensed Assisted Access (LTE LAA) is shortly about applying LTE Carrier Aggregation also for unlicensed spectrum. Due to an assumed high availability of unlicensed spectrum globally, LTE LAA is intended to exploit the unlicensed spectrum and thereby provide a performance boost to a licensed carrier. Moreover, LTE LAA is thought to be used especially for small cells. A Primary Cell (PCell) is always in the licensed spectrum and a Secondary Cell (SCell) may use unlicensed bands, in addition to or without SCell(s) on licensed bands. LTE LAA is a variant of inter-band aggregation LTE LAA is also called LTE-Unlicensed (LTE-U) and both terms are used in the current document.
Moreover, in a further scenario, relating to 5G, the same disadvantage has also been identified as described in the following.
In 5G, a tight integration of air interfaces is envisioned where, for example, common higher layer protocol layers are used on the top of air-interface specific lower layer protocols. The consequence of such integration is that a radio bearer would be in principle transparent to the core network i.e. it is not known to the core network which access is being used, what performance per access is being achieved and how much data is going via each access.
An example of tight integration between LTE (Evolution) and new “5G RAT”, e.g. New Radio (NR) access, in a combined base station for these accesses is shown in FIG. 6. Functionality over the radio interfaces is divided into asynchronous and synchronous functionality. One example of this is that the RLC, MAC and PHY functionalities are kept together since their functionalities are considered as forming a synchronous functional group and RRC and PDPC are kept together since their functionalities are considered as asynchronous. Therefore, the new functional split of the eNB gives two new functional entities, or logical network elements: eNB-a (as eNB-asynchronous) and eNB-s (as eNB-synchronous). In this case the eNB-a can contain common support for both control and user plane for the asynchronous functions for both LTE (Evolution) and new “5G RAT”. Furthermore, this also enables that the synchronous functions may be RAT-specific, for example different for LTE RAT and 5G RAT. This case is shown in FIG. 6 where the eNB-a is called “5G & LTE eNB-a” and the eNB-s are called “LTE eNB-s1” and “5G eNB-s2”.
In these three scenarios, a problem may be that charging cannot be performed while taking into account which air interface, or radio spectrum that is used by a UE. This limits the way operators can define their business model and charge subscribers flexibly according to their usage of different air interfaces and/or radio spectrums.
As an example, operators may wish to have a more flexible charging, e.g. in terms of differentiation between e.g. WLAN and 3GPP, LTE and 5G, or licensed and un-licensed spectrum.